The aim of this proposal is to study genes that control early mammalian development. The approach to be taken is founded on the observation that a 180 bp sequence, known as the "homeobox," is found in several of the genes that are known to regulate development in Drosophila. This highly conserved sequence is also present in approximately 10 copies in the mammalian genome, and mouse genomic clones containing homeoboxes have been isolated. Preliminary studies suggest that at least one of the "homeobox-containing genes" that has been isolated is expressed differentially during the development of the mouse embryo. The working hypothesis upon which this proposal is based is that the homeobox identifies genes that have a role in the control of developmental processes in mammals. The first specific aim of these studies is to carry out Northern blot analyses to determine at what stages of mouse embryonic development transcripts from these genes are expressed. Information gained from this study will be useful in carrying out the second specific aim, which is to isolate from cDNA librares, clones that encode these transcripts. The availability of such clones will make possible a study of the structure of these homeobox-containing genes. The third specific aim is to determine which cells in the developing embryo actively express homeobox-containing mRNAs by in situ hybridization with the cDNA probes. The cDNA clones will also be used to carry out the fourth specific aim, which is to obtain quantities of the homeobox-containing gene products in bacterial and mammalian expression vector systems. The proteins thus obtained will be used to raise specific antibodies against the gene products and to study their function. The antibodies will be used to study the subcellular localization of the gene products in developing embryos. Finally, the fifth specific aim is to determine the position of the homeobox-containing genes in the mouse linkage map and attempt to identify mutant alleles of these genes. In addition, the effects of induced alterations in homeobox-containing gene expression on the development of the mouse embryo will be evaluated. Taken together, the results of these studies should help to determine the function of these genes in the developing mouse embryo and may lead to a better understanding of how development in mammals is controlled.